Biotech has developed and is producing a number of products for the detection of antibodies to HTLV-III in human sera. The company has also developed non-radioactive techniques for tagging DNA probes with haptens, so that they may be detected using enzyme-linked antibodies. Such probes are potentially useful for the detection of viruses in infected cells and specifically the detection of HTLV-III RNA in human lymphocytes. Direct tests for HTLV-III are urgently needed to follow up the antibody detection tests, and we estimate the potential market for such a DNA probe-based kit to be about $10 million per year. Our goals for Phase II are to determine the best format for an HTLV-III DNA probe test, package the format into a kit and test the actual kit in preparation for FDA licensing. Two formats, spot-blots on nitrocellulose and in situ hybridization on microscope slides, will be compared for sensitivity, simplicity of performance, time required to complete the test, ease of interpretation and ease and cost of manufacturing. The format which we judge to be best will be incorporated into a clinical laboratory test kit of one or more sizes. The kit should be available for research use only before the end of Phase II. At the end of Phase II, we expect the kit to be ready for clinical trials.